1. Field of the Invention
The present invention relates to a vehicle height adjustment device which automatically adjusts the height of the vehicle relative to the wheels to a target value, and more particularly, to a vehicle height adjustment device which automatically terminates its vehicle height adjustment operation when an abnormal operation occurs, and restarts its operation when the cause of the abnormal operation disappears.
2. Description of the Prior Art
Vehicle height adjustment devices have been developed with the ability to terminate the operation thereof, and adjustment in response to an abnormal operation thereof, and restart the operation when the cause of the abnormal operation has disappeared, as is described, for example, in Japanese Patent Laid Open Publication Sho 58-49507 (1983).
This technology has a logic circuit which stops the operation of vehicle height adjustment when a target vehicle height is not attained even after the vehicle height adjustment device has been operated for a certain period, and thereafter restarts the device if and when the target vehicle height is attained.
Generally, however, abnormal operations in the vehicle height adjustment device are either due to faults in the device itself, or abnormalities in the conditions under which it is being used. Abnormalities in the conditions of use include for example cases where the vehicle is overloaded, or is on extremely uneven ground. In this case, after a temporary operation failure, it is desirable that when the normal operation conditions have been restored for the operation of vehicle height adjustment, the control device is automatically restarted. On the other hand, it is not desirable that the control device be restarted if the cause of the operation failure has not yet been removed.
In the above-mentioned prior art, when the operation was terminated because the target vehicle height was not attained even though the system had been operated for a certain predetermined period, if the target vehicle height is attained thereafter even for a moment, for any reason whatsoever, the operation of the system will be immediately restarted.
Therefore, if the vehicle is still overloaded or there is a fault in the device itself that it has terminated operation, and the vehicle body bounds slightly, then the system operation will be restarted. Since the system has been spuriously restarted, there still remains a heavy load on the device or other system failure (such as leakage) which lead to further failures.